This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The work in my laboratory is focused on the structural characterization of novel enzymes and protein complexes. We are currently looking at several different enzymes/systems for these studies. Our work on novel enzymes is being conducted in collaboration with Dr. David Palmer (UofS). We have two projects underway with his group, to determine the structures of *2-Succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate (SHCHC) synthase (MenD)*, and important enzyme in the vitamin K biosynthetic pathway, and *inositol dehydrogenase (IDH)*, a protein that has diverse substrate recognition. Protein-protein interactions are essential for the proper functioning of all cellular systems. In general, there are two types of protein-protein interactions, tight-binding systems such as those seen with antibody:antigen interactions and the formation of protein complexes, and transient or weak binding interactions such as are seen between two proteins interacting in an enzymatic process. The protein-protein interaction system that we are currently studying is the thioredoxin system. Our current research objectives are to probe the interactions between thioredoxin (Trx) and thioredoxin reductase (TrxR) from different species, to characterize the interactions that are important for binding and to examine the way these enzymes are compensating for temperature differences and other evolutionary pressures to maintain their ability to interact with each other.